Water and Solute Permeability of Plant Cuticles: Measurement and ...

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170 6 Diffusion of Non-Electrolytes A specific /A projected 160 140 120 100 80 60 40 20 Picea abies Pinus sylvestris Picea pungens Abies alba y-Intercept x 1012 0 0 20 40 60 80 100 120 140 160 180 (mol/mm) Fig. 6.10 Correlation between y-intercept measured by a penetration experiment (Fig. 6.8) with ratio Aspecific/Aprojected estimated from sorption of PCP in conifer needles. The slope is 0.82. (Data taken from Schreiber and Schönherr 1992b) more epicuticular wax (Table 6.6). Thus, specific surface areas estimated from BET isotherms are overestimates and not very precise. Monolayer formation and sorption in waxes are related, and the sum of both constitutes the driving force of cuticular penetration. The y-intercept measured by steady state experiments (Figs. 6.5 and 6.9) characterise the sizes of the two compartments in which lipophilic chemicals are reversibly sorbed. Their sizes are proportional to the amount of wax and cutin and to partition coefficients of solutes (Table 6.5). CPT1 and CPT2 are intermediate compartments from which solutes penetrate into apoplast and symplast. Rates of penetration into CPT3 are proportional to the sizes of CPT1 and CPT2. The absolute amounts of solutes sorbed reversibly in CPT1 and CPT2 are proportional to the solute concentration in the donor. This follows from the definition of the partition coefficient. For this reason, permeance is also proportional to the y-intercept. 6.2.2.5 Evaluation of Compartmental Analysis Data generated using barley leaves and conifer needles demonstrate that steady state penetration in combination with compartmental analysis is a powerful tool for measuring and interpreting data on foliar penetration. Measurements are simple, and can be made with detached leaves if not too large. Isolating cuticles is not required, and leaves with stomata can be used. When stomata open in the light, infiltration of the intercellular space is possible, but this can be avoided when donor solutions have Abies koreana
6.2 Steady State Penetration 171 a relatively high surface tension. With leaves of Zebrina it was shown that infiltration of stomata will not occur if surface tension is 35mN m −1 or higher (Schönherr and Bukovac 1972a). This even permits using low concentrations of surfactants to improve wetting of leaf surfaces. There is no need to worry that infiltration of stomata occurs but is not noticed. Infiltration can be detected with the bare eye, because dark spots will be seen in incident light which look bright in transmitted light. This phenomenon is due to a local change in refractive index when intercellular air spaces are filled with water. Diffusion of solutes into the wound caused by cutting off the leaf at the petiole is no problem, because it can be quantified and corrected for easily (Fig. 6.4). The donor solution must be agitated to ensure mixing. If donor solutions are at ambient pressure (vessels open), there is no need to worry about pressure forcing liquid into open stomata. When working with barley leaves and conifer needles this was not a problem, even though test tubes were tightly closed. So far the methods have been used only with lipophilic solutes. There is no reason why it should not work with polar non-electrolytes or with ions. With polar solutes the sizes of CPT1 and CPT2 are probably very small, and the y-intercept is close to zero. Permeance can be calculated from the slope of the penetration or the desorption graphs which are superimposed if sorption in wax and cuticles is insignificant (cf. Fig. 6.13). With leaves that are easily wetted, a surface film of donor can be estimated by desorption, and all donor solution will be washed off with the first change of desorption medium. This offers the possibility to measure permeability of delicate leaves such as Arabidopsis. The method works well as long the leaf surface is not densely populated by microorganisms, as was observed when working with older conifer needles sampled from forest trees (Schreiber and Schönherr 1992c). Plants grown in growth chambers or greenhouses usually have clean surfaces. In any case, it is good practice to check for surface contaminations. 6.2.3 Steady State Penetration into Leaf Disks Using the Well Technique Broadleaved plants can have very large leaves which are not suitable for the submersion technique. In these cases, penetration can be measured using a droplet method. Small droplets of donor solutions are placed on the upper or lower surfaces of leaves attached to or dissected from plants. This approach is much closer to the situation after spray application to the foliage, and this is often considered an advantage. However, experiments of this kind are beset with severe problems, as penetration proceeds under uncontrolled conditions. For instance, concentrations and pH of donor solutions change during droplet drying, temperature of the donor differs from leaf and surrounding air, contact area between donor and leaf is difficult to estimate precisely and may vary with time, and the solutes may solidify or crystallise. These problems are almost as bad in growth chambers than in the field.
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Water and Solute Permeability of Pl
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Professor Dr. Lukas Schreiber Ecoph
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vi Preface This is not a review abo
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Contents 1 Chemistry and Structure
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Contents xi 4.6.3 Diffusion Coeffic
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Contents xiii 7.4.2 Effects of Plas
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2 1 Chemistry and Structure of Cuti
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10 1 Chemistry and Structure of Cut
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Chapter 2 Quantitative Description
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2.1 Models for Analysing Mass Trans
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2.3 Steady State Diffusion Across a
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2.4 Steady State Diffusion of a Sol
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2.4 Steady State Diffusion of a Sol
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2.5 Diffusion Across a Membrane wit
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2.5 Diffusion Across a Membrane wit
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2.6 Determination of the Diffusion
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Solutions 51 2.7 Summary In this ch
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Chapter 3 Permeance, Diffusion and
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3.1 Units of Permeability 55 3.1.1
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3.1 Units of Permeability 57 identi
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3.3 Partition Coefficients 59 The d
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Chapter 4 Water Permeability All te
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4.1 Water Permeability of Synthetic
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4.2 Isoelectric Points of Polymer M
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4.2 Isoelectric Points of Polymer M
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4.3 Ion Exchange Capacity 69 The hi
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4.3 Ion Exchange Capacity 71 has an
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4.3 Ion Exchange Capacity 73 Counte
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4.4 Water Vapour Sorption and Perme
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4.4 Water Vapour Sorption and Perme
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4.5 Diffusion and Viscous Transport
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4.6 Water Permeability of Isolated
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220 7 Accelerators Increase Solute
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Chapter 8 Effects of Temperature on
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8.1 Sorption from Aqueous Solutions
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8.1 Sorption from Aqueous Solutions
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8.2 Solute Mobility in Cuticles 239
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8.3 Water Permeability in CM and MX
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8.3 Water Permeability in CM and MX
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8.4 Thermal Expansion of CM, MX, Cu
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Problems 257 E D (kJ/mol) DH S (kJ/
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Chapter 9 General Methods, Sources
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9.2 Testing Integrity of Isolated C
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9.4 Distribution of Water and Solut
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9.6 Cutin and Wax Analysis and Prep
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9.7 Measuring Water Permeability 26
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9.8 Measuring Solute Permeability 2
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276 Appendix A Abbreviations (conti
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278 Appendix A Symbols (continued)
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280 Appendix B Physico-chemical pro
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Appendix C Index of Plants Botanica
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References Abraham MH, McGowan JC (
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References 287 Doty PM, Aiken WH, M
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References 289 Kolattukudy P (2004)
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References 291 Sabljic A, Güsten H
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References 293 Schreiber L, Schönh
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Index 2,4-D, 46 2,4-Dichlorophenoxy
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Index 297 leaf disks, 130 leaf surf
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Index 299 water molar volume, 110 p
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Water and Solute Permeability of Plant Cuticles: Measurement and ...

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